Twenty-one times this season, Dave Roberts has had to address reporters after a Dodgers loss. The first 20 times, he struck a similar tone. Within every answer was a fundamental confidence that his club would eventually find its desired path.

On Thursday night at Dodger Stadium, the Dodgers lost their 21st game, and Roberts struggled for words as he sat for his press conference.

“I usually have an answer,” he began.

He had just finished watching another poor performance. Facing the tanking Cincinnati Reds, who already fired their manager weeks ago, the Dodgers scored only once in a 4-1 loss. They forced starter Tyler Mahle onto the ropes at 63 pitches through two innings, then let him slither past. They managed one hit after the third inning, a Kiké Hernández pinch-hit single, and then squandered six solid innings from Walker Buehler. Roberts was fed up.

“It’s very frustrating, and I expect those guys in the clubhouse to be frustrated as...